Recently, a so-called memory card (an example of recording media) formed by packaging a nonvolatile memory such as a flash memory in a card form is widely known. Memory cards are rapidly spread as data storage media to be used in digital devices such as digital cameras and portable music players. Since there is no unified specification for the memory cards, various memory cards are on the market place. Examples of the memory cards on the market place are as follows: a compact flash (registered trademark, hereinafter referred to as a “CF”); smart media (registered trademark, hereinafter referred to as an “SM”); a memory stick (registered trademark, hereinafter referred to as an “MS”); and an SD memory card (registered trademark, hereinafter referred to as an “SD”).
The PC can access the memory card by using a memory card reader/writer (an example of the peripheral device, hereinafter referred to as a “reader/writer”) for reading from and writing on the memory card connected to the PC. Thereby, data communication can be made between the PC and the memory card. As such a reader/writer, U.S. Patent Application Publication 2005/0023339 A1 discloses a single slot type having one slot in which a memory card is inserted and a multi-slot type having a plurality of slots capable of reading and writing data from and on a plurality of memory cards.
It has become common that the above-described reader/writer performs data transfer to the PC by serial communication from the background that data transfer capacity has dramatically increased due to the spread of multimedia. However, from a viewpoint of easiness in handling of a plurality of storage media, there are many devices that adopt a method, as a data access control, having been used in arbitration/access control of peripheral devices for parallel communication. A typical example includes a system designed so as to make data communication between the PC and the reader/writer based on a protocol defined by so-called SCSI standards (hereinafter, also referred to as SCSI protocol). The SCSI standards are a communication protocol standardized by ANSI (American National Standard Institute) and internationally accepted. This protocol can increase the generality of the PC and the reader/writer, so that it is widely used. In the description given below, SCSI standards indicate SCSI-2, basically.
In the SCSI protocol, the PC as a host device functions as an initiator provided with authority to start a communication event and determines the peripheral device as a communication target of the host device. Commands for executing the communication event are successively issued from the PC to the peripheral device, and on the other hand, the peripheral device that has received the issued commands successively executes processes corresponding to the commands (for example, data reading, writing, erasing, and various accompanying processes) and replies to the host device with response information in accordance with the results of execution. In the SCSI specifications, only the host device is allowed to issue the commands for administering the execution of the communication event. That is, the transmission direction of the commands is regulated to one direction from the host device to the peripheral device.
As described above, although the SCSI communication is bidirectional communication between the PC and the peripheral device, the transmission direction of commands for administering the communication event is regulated to one direction from the PC to the peripheral device. Therefore, the PC as an initiator always seizes the initiative with the communication processing start. That is, as long as following the SCSI protocol, it is impossible to inversely transmit commands for starting the communication event from the peripheral device to the host device, and there was no method for voluntarily starting a specific communication event on the peripheral device. For example, when the PC reads an image data file stored in a memory card loaded in the reader/writer or the image data file is saved in a storage device on the PC such as a hard disk drive (HDD), a user must always perform an operation for reading or writing on the PC (that is, command execution input). Therefore, even if a memory card storing an image data file is loaded in a reader/writer disposed remote from a PC, when a user wants to save the image data file in the PC, the user cannot perform an operation for saving unless he/she goes to the PC location, and this is very inconvenient for the user.